Multiple projectors are sometimes combined to form multiple-projector systems to increase the brightness of a projected image field and/or to increase the size of a projected image field. For example, to increase the brightness of a projected image field, the image fields of the respective projectors of the system are superimposed (e.g., or stacked) on each other to form a stacked image field. An example of increasing the size of a projected image field involves displaying the image fields of the respective projectors of the system side by side (or tiling the image fields of the respective projectors of the system), e.g., with portions of the respective image fields overlapping, to form a tiled image field, with each projector corresponding to a tile. For some applications, the brightness of each tile of the tiled image field may be increased by stacking the image fields of a plurality of projectors corresponding to that tile.
The projectors of multiple-projector systems are typically aligned with each other to form substantially seamless displays, e.g., so that a line appears substantially continuous across the image fields of the respective projectors. Aligning the respective projectors usually involves executing a rather complex, time-intensive calibration procedure. For example, each projector displays a calibration pattern, and one or more image-capturing devices, such as one or more cameras, record the calibration pattern for each projector. The recorded calibration patterns are then used to create a mapping between the pixels of each projector and where the corresponding pixels land on the screen. The mapping is then used to align the projectors to create the desired display. For example, the projectors are typically aligned to project data only on a portion of their respective image fields that corresponds to an image field that is common to or is an intersection of the image fields of the respective projectors of the system and that contains the desired display. However, projector alignment can shift over time, resulting in degradation of the stacked or tiled image projected by the multiple-projector system. Therefore, it may be necessary to perform a rather time-consuming and complex recalibration of the system.